U.S. patent application number 09/875397 was filed with the patent office on 2002-12-19 for method and apparatus for antenna diversity in a wireless communication system.
Invention is credited to Wallace, Mark, Walton, Jay Rod.
Application Number | 20020193146 09/875397 |
Document ID | / |
Family ID | 25365728 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020193146 |
Kind Code |
A1 |
Wallace, Mark ; et
al. |
December 19, 2002 |
Method and apparatus for antenna diversity in a wireless
communication system
Abstract
Method and apparatus for negotiating a transmission scenario in
a mixed mode spectrum wireless communication system capable of both
MISO and SISO traffic. The transmitter determines an antenna
diversity configuration for a given communication link and applies
a transmission scenario. The base station queries the remote
station for antenna diversity status. In response to the antenna
diversity status information, the base station determines and
applies a transmission scenario. In one embodiment, a base station
generates composite MIMO transmissions to multiple SISO mobile
stations.
Inventors: |
Wallace, Mark; (Bedford,
MA) ; Walton, Jay Rod; (Westford, MA) |
Correspondence
Address: |
Sarah Kirkpatrick, Manager
Intellectual Property Administration
QUALCOMM Incorporated
5775 Morehouse Drive
San Diego
CA
92121-1714
US
|
Family ID: |
25365728 |
Appl. No.: |
09/875397 |
Filed: |
June 6, 2001 |
Current U.S.
Class: |
455/562.1 ;
375/347; 455/101; 455/272 |
Current CPC
Class: |
H04B 7/0604 20130101;
H04B 7/0417 20130101; H04L 5/0028 20130101; H04B 7/0865 20130101;
H04L 5/0023 20130101; H04B 7/0678 20130101; H04B 7/0697 20130101;
H04B 7/0669 20130101; H04L 5/006 20130101; H04B 7/0871 20130101;
H04B 7/0689 20130101; H04B 7/0628 20130101; H04L 5/0007 20130101;
H04B 7/082 20130101; H04B 7/0643 20130101 |
Class at
Publication: |
455/562 ;
455/101; 455/272; 375/347 |
International
Class: |
H04M 001/00 |
Claims
What is claimed is:
1. A base station apparatus comprising: an antenna array; and a
diversity controller coupled to the antenna array, operative for
determining a transmission scenario based on the configuration of a
given communication link.
2. An apparatus as in claim 1, wherein the diversity controller is
operative to query a mobile station for diversity capability of the
mobile station to establish a first communication link with the
mobile station.
3. An apparatus as in claim 2, wherein the diversity controller is
operative to determine the transmission scenario according to the
antenna configuration of the mobile station and the antenna
configuration of the base station.
4. An apparatus as in claim 3, wherein if the mobile station has a
single antenna the diversity controller is operative to transmit to
the mobile station on a single antenna.
5. An apparatus as in claim 3, further comprising: a delay element
coupled between a first antenna element and a second antenna
element of the antenna array, wherein if the mobile station has a
single antenna the apparatus is operative to transmit to the mobile
station using the first and second antenna elements.
6. An apparatus as in claim 3, wherein: the antenna array comprises
a first antenna element and a second antenna element, during a
first time period the first antenna element transmits a first
signal and the second antenna element transmits a second signal,
and during a second time period the first antenna transmits a third
signal that is a function of the second signal and the second
antenna transmits a fourth signal that is a function of the first
sign.
7. An apparatus as in claim 3, further comprising: a first coding
unit; and a switching means for coupling the first coding unit to
the antenna array.
8. An apparatus as in claim 1, wherein for a multiple input
multiple output capable receiver the transmission scenario is
determined as a function of a channel quality metric.
9. An apparatus as in claim 1, wherein the transmission scenario is
determined as a function of receiver capability.
10. A base station apparatus comprising: an antenna array; a
control processor for processing computer-readable instructions;
and a memory storage device coupled to the control processor,
operative to store a plurality of computer-readable instructions,
comprising: a first set of instructions for requesting antenna
diversity status of the first communication link; a second set of
instructions for determining a first transmission scenario of the
first communication link in response to the antenna diversity
status; and a third set of instructions for applying the first
transmission scenario to the first communication link.
11. An apparatus as in claim 10, wherein for a multiple input
multiple output capable receiver the transmission scenario is
determined as a function of the channel quality.
12. An apparatus as in claim 10, wherein antenna diversity status
comprises the number of receive antennas at a receiver of the first
communication link.
13. A method for communication in a wireless communication system,
the method comprising: receiving antenna diversity status
information for a first communication link; and determining a
configuration of the first communication link in response to the
antenna diversity status information; and applying a transmission
scenario to the first communication link.
14. A method as in claim 13, further comprising: receiving antenna
diversity status information for a second communication link;
determining a second configuration of the second communication link
in response to the antenna diversity status information; and
applying a second transmission scenario to the second communication
links.
15. A method as in claim 14, wherein if the first configuration is
a single receive antenna configuration, and the second
configuration is a multiple receive antenna configuration, the
transmission scenario applies a delay to signals for the first
communication link.
16. A computer readable media embodying a method for determining a
transmission scenario in a wireless communication system, the
method comprising: querying multiple mobile users for antenna
diversity status; receiving antenna diversity status information
from at least one of the mobile users; and applying a transmission
scenario consistent with the antenna diversity status
information.
17. A mobile station apparatus comprising: a channel quality
measurement unit operative to determine a channel quality; and a
diversity controller coupled to the channel quality measurement
unit, operative for determining a transmission scenario based on
the channel quality.
18. A mobile station apparatus as in claim 17, wherein the channel
quality is a function of a ratio of carrier to interference of
received signals.
19. A mobile station apparatus as in claim 17, further comprising:
a receiver coupled to channel quality measurement unit and the
diversity controller, wherein the mobile station apparatus
configures the receiver consistent with the transmission
scenario.
20. A method for receiving communications in a wireless
communication system, comprising: receiving a communication signal;
measuring a channel quality based on the received communication
signal; and determining a transmission scenario based on the
channel quality.
21. A wireless communication system, comprising: transmit antenna
means; receive antenna means operative for receiving communications
from the transmit antenna means; and a diversity controller coupled
to the transmit antenna means, operative for determining a
transmission scenario based on the configuration of a given
communication link.
Description
RELATED CO-PENDING APPLICATIONS
[0001] The present Application for Patent is related to "METHOD AND
SYSTEM FOR INCREASED BANDWIDTH EFFICIENCY IN MULTIPLE
INPUT--MULTIPLE OUTPUT CHANNELS" by John Ketchum, having U.S.
patent application Ser. No. 09/737,602, filed Jan. 5, 2001,
assigned to the assignee hereof and expressly incorporated by
reference.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to wireless data
communication. More particularly, the present invention relates to
a novel and improved method and apparatus for antenna diversity in
a wireless communication system.
[0004] 2. Background
[0005] To improve the quality of wireless transmissions,
communication systems often employ multiple radiating antenna
elements at the transmitter to communicate information to a
receiver. Multiple antennas are desirable, as wireless
communication systems tend to be interference-limited, and the use
of multiple antenna elements reduces inter-symbol and co-channel
interference introduced during modulation and transmission of radio
signals, enhancing the quality of communications. Further, the use
of multiple element antenna arrays at both the transmitter and
receiver enhances the capacity of multiple-access communication
systems.
[0006] Each system may employ various antenna configurations,
including user terminals having only single antenna capability and
other user terminals have multiple antennas. Communications for
each type of user are processed differently. There is a need,
therefore, for high-quality, efficient communications in a mixed
mode system.
SUMMARY
[0007] A method for communication in a wireless communication
system, the method includes receiving antenna diversity status
information for a first communication link, determining of a
configuration of the first communication link in response to the
antenna diversity status information, and applying a transmission
scenario to the first communication link.
[0008] In one aspect, a base station apparatus includes an antenna
array, and a diversity controller coupled to the antenna array,
operative for determining a transmission scenario based on the
configuration of a given communication link.
[0009] In an alternate aspect, a base station apparatus includes a
control processor for processing computer-readable instructions,
and a memory storage device coupled to the control processor,
operative to store a plurality of computer-readable instructions.
The instructions include a first set of instructions for requesting
antenna diversity status of the first communication link, a second
set of instructions for determining a first transmission scenario
of the first communication link in response to the antenna
diversity status, and a third set of instructions for applying the
first transmission scenario to the first communication link.
[0010] In still another aspect, a wireless communication system
includes a base station, having a first receive antenna, a first
correlator and a second correlator coupled to the first receive
antenna, a second receive antenna, a third correlator and a fourth
correlator coupled to the first receive antenna, a first combiner
coupled to the first and third correlators, and a second combiner
coupled to the second and fourth correlators. According to one
embodiment, a first code is applied to the first correlator and a
second code, different from the first code, is applied to the
second correlator, the first code is applied to the third
correlator and the second code is applied to the fourth
correlator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a wireless communication system.
[0012] FIG. 2 is a configuration of transmitter antennas in a
wireless communication system.
[0013] FIG. 3 is a table of antenna diversity configurations in a
wireless communication system.
[0014] FIG. 4 is a mixed mode wireless communication system.
[0015] FIG. 5 is a mixed mode wireless communication system.
[0016] FIG. 6 is a model of a channel between transmitter and
receiver in a wireless communication system.
[0017] FIG. 7 is model of a channel for a Multiple Input Multiple
Output, MIMO, configuration.
[0018] FIG. 8 is a wireless communication system employing
selection diversity at a receiver.
[0019] FIG. 9 is a wireless communication system employing Maximal
Ratio Combining, MRC, type selection diversity at a receiver.
[0020] FIG. 10 is a wireless communication system configured for
transmit diversity transmissions.
[0021] FIG. 11 is a wireless communication system configured for
MIMO transmissions.
[0022] FIG. 12 is a wireless communication system capable of MIMO
and diversity transmissions.
[0023] FIG. 13 is a flow diagram of a method of mixed mode
operation of a forward link in a wireless communication system.
[0024] FIG. 14 is a flow diagram of a method of mixed mode
operation of a reverse link in a wireless communication system.
[0025] FIG. 15 is a wireless communication system employing
transmit diversity.
[0026] FIG. 16 is a wireless communication system employing
transmit diversity and spreading codes.
[0027] FIG. 17 is a base station having a distributed antenna
system for creating multi-paths in a wireless communication
system.
[0028] FIG. 18 is a base station having a mixed mode
controller.
[0029] FIG. 19 is a mixed mode wireless communication system
incorporating MIMO mobile stations and SISO mobile stations.
[0030] FIG. 20 is a mobile station adapted for operation within a
wireless communication system.
DETAILED DESCRIPTION
[0031] The use of multiple element antenna arrays at both the
transmitter and receiver is an effective technique for enhancing
the capacity of multiple-access systems. Using Multiple
Input-Multiple Output, MIMO, the transmitter can send multiple
independent data streams on the same carrier frequency to a user.
At high Signal to Noise Ratios, SNRs, the increase in throughput
approaches N times the throughput of single transmit systems
operating with Single Input-Multiple Output, SIMO, or without
receive diversity, Single Input-Single Output, SISO, where
N=min(N.sub.t,N.sub.r), with N.sub.r and N.sub.t being the number
of receiver and transmitter antennas, respectively.
[0032] In some systems it is desirable to support a mixture of user
terminal types. For example, terminals designed for voice services
only may employ a single antenna for receive and transmit. Other
devices may employ a number of receive antennas, and possibly a
number of transmit antennas as well. To support mixed mode
operation the base station must be equipped with multiple antennas
on which to transmit and receive. The table of FIG. 3 gives the
matrix of operating modes for terminal traffic including SISO,
SIMO, Multiple Input-Single Output, MISO, and MIMO that can be
supported by a MIMO capable network.
[0033] In multiple access systems it is desirable that all four
modes of operation be supported. For performance reasons it is
usually desirable to employ diversity techniques (i.e., SIMO and
MISO) whenever possible since these schemes typically outperform
SISO methods. On the uplink, also referred to as the reverse link,
diversity techniques can be supported by placing multiple receive
antennas at the base stations. On the downlink however, it implies
that some form of transmit diversity be used when transmitting to
single receive antenna devices (i.e., MISO). Because MISO operation
requires different receiver processing than SISO operation, it is
possible that certain systems may have a requirement to also
support SISO operation for a fraction of the terminals.
[0034] In Time Division Multiple Access, TDMA, and Frequency
Division Multiple Access, FDMA, systems it is possible to segregate
the SISO downlink traffic from the rest of the traffic by providing
those services on separate time slots or frequencies. So, mixed
mode operation is relatively easy to accommodate in these
systems.
[0035] In CDMA systems it is not as easy to isolate SISO traffic
from traffic using other modes. In CDMA systems, users are assigned
different spreading codes that perform a similar function as
frequency sub-channels in the FDMA case or time slots in the TDMA
case. In some cases, the spreading codes are designed to be
mutually orthogonal so that interference from other users is zero.
As long as the channel is non-dispersive (i.e., no resolvable
multipath), the orthogonality property holds and users do not
interfere with one another. In this case it is possible to use SISO
for a user on one code channel and MISO or MIMO for users on other
code channels. However, when the channel becomes time dispersive,
orthogonality is lost and interference power from other users is no
longer zero. Channels become dispersive as a result of multipath
signal propagations that differ from one another by more than one
spreading chip duration. When propagation paths differ by more than
one spreading chip in duration, they can be independently
demodulated using a RAKE receiver as is well known in the art and
described in detail in U.S. Pat. No. 5,109,390, entitled "Diversity
Receiver in a CDMA Cellular Telephone System", assigned to the
assignee of the present invention and hereby expressly incorporated
by reference herein. In addition, equalizer receiver structures can
also be used to demodulate signals experiencing multipath
propagation.
[0036] In traditional CDMA systems, a loss in orthogonality on the
downlink is not necessarily catastrophic since the signal and
interference terms are correlated on each of the delay components.
Suppose the channel response is given as
H.sub.0(t)=h.sub.0,0(t)+h.sub.0,- 1(t-T), where h.sub.0,0 is the
direct path and h.sub.0,1 is the reflected path between the
transmit antenna 0 and the user terminal antenna. Further assume
that h.sub.0,0 and h.sub.0,1 are not highly correlated. The RAKE
receiver is essentially a matched filter in this case, so the
average SNR ratio, .gamma., can be expressed as: 1 SISO = ( W I o R
) [ + I 0 + + I 0 ] , ( 1 )
[0037] wherein W is the operating bandwidth, R is the data rate,
I.sub.0 is the total power of the downlink, .phi. is the fraction
of total power allocated to the user, and .eta. is the thermal
noise power. Additionally defined are:
.alpha.=E{.vertline.h.sub.0,0.vertline..sup.2} (2)
[0038] and
.beta.=E{.vertline.h.sub.0,1.vertline..sup.2} (3)
[0039] wherein E{ } signifies expected value. Inspection of this
SISO SNR expression of equation (1) shows that even though the
direct and reflected paths of the channel destroy orthogonality,
they provide a form of implicit diversity. That is, the
interference power in the denominator of the first term in
brackets, .beta.I.sub.0, is identically correlated with the signal
power in the numerator of the second term. A similar relationship
exists for the other path. Assuming the data rate and power
allocation are matched appropriately, the interference power caused
by the delay spread does not significantly contribute to the
overall error rate. That is, the primary error event is when both
paths fade into the noise.
[0040] Now, consider what happens to the SISO receiver when another
transmit antenna is used to accommodate users employing MISO and/or
MIMO. Using a similar channel model as above for the second
transmit antenna results in a channel response of
H.sub.1(t)=h.sub.1,0(t)+h.sub.1,1(t-T), and the SNR at the RAKE
receiver output now becomes: 2 mixed_mode = ( W I o R ) [ + I 0 + I
1 + + I 0 + I 1 ] , ( 4 )
[0041] Inspection of the SISO SNR expression given in equation (4)
shows that the power from transmit antenna 1, I.sub.1, now present
an independent fading interference term in the denominator of both
terms in the brackets. In this case, the primary error event is the
desired signal from antenna 0 fading relative to the interference
power emitted from antenna 1. So in mixed mode operation (i.e., one
transmitter communicating with a MIMO and/or MISO user and also
with a SISO user), the interference power from the additional
antennas can seriously degrade the performance of SISO
terminals.
[0042] In one embodiment, a CDMA system solves this problem using a
form of transmit diversity (e.g., MISO) to accommodate single
receive antenna users when mixed mode services are offered. Various
alternate MISO approaches to solving this problem are described
herein.
[0043] FIG. 1 is a diagram of a communications system 100 that
supports a number of users and is capable of implementing at least
some aspects and embodiments of the invention. System 100 provides
communication for a number of cells 102A through 102G, each of
which is serviced by a corresponding base station 104A through
104G, respectively. In the exemplary embodiment, some of base
stations 104 have multiple receive antennas and others have only
one receive antenna. Similarly, some of base stations 104 have
multiple transmit antennas, and others have single transmit
antennas. There are no restrictions on the combinations of transmit
antennas and receive antennas. Therefore, it is possible for a base
station 104 to have multiple transmit antennas and a single receive
antenna, or to have multiple receive antennas and a single transmit
antenna, or to have both single or multiple transmit and receive
antennas.
[0044] Terminals 106 in the coverage area may be fixed (i.e.,
stationary) or mobile. As shown in FIG. 1, various terminals 106
are dispersed throughout the system. Each terminal 106 communicates
with at least one and possibly more base stations 104 on the
downlink and uplink at any given moment depending on, for example,
whether soft handoff is employed or whether the terminal is
designed and operated to (concurrently or sequentially) receive
multiple transmissions from multiple base stations. Soft handoff in
CDMA communications systems is well known in the art and is
described in detail in U.S. Pat. No. 5,101,501, entitled "Method
and system for providing a Soft Handoff in a CDMA Cellular
Telephone System", which is assigned to the assignee of the present
invention and incorporated by reference herein.
[0045] The downlink refers to transmission from the base station to
the terminal, and the uplink refers to transmission from the
terminal to the base station. In the exemplary embodiment, some of
terminals 106 have multiple receive antennas and others have only
one receive antenna. Similarly, some of terminals 106 have multiple
transmit antennas, and others have single transmit antennas. There
are no restrictions on the combinations of transmit antennas and
receive antennas. Therefore, it is possible for a terminal 106 to
have multiple transmit antennas and a single receive antenna or to
have multiple receive antennas and a single transmit antenna or to
have both single or multiple transmit or receive antennas. In FIG.
1, base station 104A transmits data to terminals 106A and 106J on
the downlink, base station 104B transmits data to terminals 106B
and 106J, base station 104C transmits data to terminal 106C, and so
on.
[0046] The use of multiple antennas at the transmitter and/or
receiver is referred to as antenna diversity. FIG. 2 illustrates a
physical configuration of multiple antennas at a transmitter. The
four antennas are each spaced at a distance "d" from the next
adjacent antenna. The horizontal line gives a reference direction.
Angles of transmission are measured with respect to this reference.
The angle ".alpha." corresponds to an angle of a propagation path
with respect to the reference within a 2-D plane as illustrated. A
range of angles with respect to the reference is also illustrated.
The position and angle of propagation define the transmission
pattern of the antenna configuration. Transmit antenna diversity
allows directional antennas to form a directed beam for a specific
user or to form multi-path signals having sufficient separation for
the receiver to identify the constituent components.
[0047] The receiver may also employ antenna diversity. In one
embodiment a rake receiver processes multi-path signals in
parallel, combining the individual signals to form a composite,
stronger signal. For a given communication link, the receiver
and/or transmitter may employ some type of antenna diversity.
[0048] Diversity reception refers to the combining of multiple
signals to improve SNR of a system. Time diversity is used to
improve system performance for IS-95 CDMA systems. Generally,
buildings and other obstacles in built-up areas scatter the signal.
Furthermore, because of the interaction between the several
incoming waves, the resultant signal at the antenna is subject to
rapid and deep fading. Average signal strength can be 40 to 50 dB
below the free-space path loss. Fading is most severe in heavily
built-up areas in an urban environment. In these areas, the signal
envelope follows a Rayleigh distribution over short distances and a
lognormal distribution over large distances.
[0049] Diversity reception techniques are used to reduce the
effects of fading and improve the reliability of communication
without increasing either the transmitter's power or the channel
bandwidth.
[0050] The basic idea of diversity receptions is that, if two or
more independent samples of a signal are taken, these samples will
fade in an uncorrelated manner. This means that the probability all
the samples being simultaneously below a given level is much lower
than the probability of any individual sample being below that
level. The probability of M samples all being simultaneously below
that level is p.sup.M, where p is the probability that a single
sample is below that level. Thus, we can see that a signal composed
of a suitable combination of the various samples will have much
less severe fading properties than any individual sample.
[0051] In principle, diversity reception techniques can be applied
either at the base station or at mobile station, although each type
of application has different problems that must be addressed.
Typically, the diversity receiver is used in the base station
instead of the mobile station. The cost of the diversity combiner
can be high, especially if multiple receivers are required. Also
the power output of the mobile station is limited by its battery
life. The base station, however, can increase its power output or
antenna height to improve coverage to a mobile station. Most
diversity systems are implemented in the receiver instead of the
transmitter since no extra transmitter power is needed to install
the receiver diversity system. Since the path between the mobile
station and the base station is assumed to be approximately
reciprocal, diversity systems implemented in a mobile station work
similarly to those in base station.
[0052] A method of resolving multi-path problems uses wide band
pseudorandom sequences modulated onto a transmitter using other
modulation methods (AM or FM). The pseudorandom sequence has the
property that time-shifted versions are almost uncorrelated. Thus,
a signal that propagates from transmitter to receiver over
multi-path (hence multiple different time delays) can be resolved
into separately fading signals by cross-correlating the received
signal with multi time-shifted versions of the pseudorandom
sequence. In the receiver, the outputs are time shifted and,
therefore, must be sent through a delay line before entering the
diversity combiner. The receiver is called a RAKE receiver since
the block diagram looks like a garden rake.
[0053] When the CDMA systems were designed for cellular systems,
the inherent wide-bandwidth signals with their orthogonal Walsh
functions were natural for implementing a RAKE receiver mitigates
the effects of fading and is in part responsible for the claimed
10:1 spectral efficiency improvement of CDMA over analog
cellular.
[0054] In the CDMA system, the bandwidth (1.25 to 15 MHz) is wider
than the coherence bandwidth of the cellular or Personal
Communication System, PCS, channel. Thus, when the multipath
components are resolved in the receiver, the signals from each tap
on the delay line are uncorrelated with each other. The receiver
can then combine them using any of the combining schemes. The CDMA
system then uses the multipath characteristics of the channel to
its advantage to improve the operation of the system.
[0055] The combining scheme used governs the performance of the
RAKE receiver. An important factor in the receiver design is
synchronizing the signals in the receiver to match that of the
transmitted signal. Since adjacent cells are also on the same
frequency with different time delays on the Walsh codes, the entire
CDMA system must be tightly synchronized.
[0056] A RAKE receiver uses multiple correlators to separately
detect the M strongest multipath components. The relative
amplitudes and phases of the multipath components are found by
correlating the received waveform with delayed versions of the
signal or vice versa. The energy in the multipath components can be
recovered effectively by combining the (delay-compensated)
multipath components in proportion to their strengths. This
combining is a form of diversity and can help reduce fading.
Multipath components with relative delays of less than
.DELTA.t=1/B.sub.w cannot be resolved and, if present, contribute
to fading; in such cases forward error--correction coding and power
control schemes play the dominant role in mitigating the effects of
fading.
[0057] Denoting the outputs of the M correlators as Z.sub.1,
Z.sub.2, . . . , and Z.sub.M, and the weights of the corresponding
outputs as a.sub.1, a.sub.2, . . . a.sub.M, respectively, the
composite signal {overscore (Z)} is given as 3 Z _ = k = 1 M a k Z
k .
[0058] The weighting coefficients are based on the power or the SNR
from each correlator output. If the power or SNR is small from a
particular correlator, it is assigned a small weighting factor. The
weighting coefficients, a.sub.k, are normalized to the output
signal power of the correlator in such a way that the coefficients
sum to unity, e.g., 4 a k = Z k 2 k = 1 M Z k 2 .
[0059] In CDMA cellular/PCS systems, the forward link (BS to MS)
uses a three-finger RAKE receiver, and the reverse link (MS to BS)
uses a four-finger RAKE receiver. In the IS-95 CDMA system, the
detection and measurement of multipath parameters are performed by
a searcher-receiver, which is programmed to compare incoming
signals with portions of I- and Q- channel PN codes. Multipath
arrivals at the receiver unit manifest themselves as correlation
peaks that occur at different times. A peak's magnitude is
proportional to the envelope of the path signal. The time of each
peak, relative to the first arrival, provides a measurement of the
path's delay.
[0060] The PN chip rate of 1.2288 Mcps allows for resolution of
multipath components at time intervals of 0.814 us. Because all of
the base stations use the same I and Q PN codes, differing only in
code phase offset, not only multipath components but also other
base stations are detected by correlation (in a different search
window of arrival times) with the portion of the codes
corresponding to the selected base stations. The searcher receiver
maintains a table of the stronger multipath components and/or base
station signals for possible diversity combining or for handoff
purposes. The table includes time of arrival, signal strength, and
the corresponding PN code offset.
[0061] On the reverse link, the base station's receiver assigned to
track a particular mobile transmitter uses the I- and Q-code times
of arrival to identify mobile signals from users affiliated with
the that base station. Of the mobile signals using the same I- and
Q-code offsets, the searcher receiver at the base station can
distinguish the desired mobile signal by means of its unique
special preamble for that purpose. As the call proceeds, the
searcher receiver is able to monitor the strengths of the multipath
components from the mobile unit to the base station and to use more
than one path through diversity combining.
[0062] FIG. 3 illustrates several antenna diversity schemes for a
given communication link between a base station and a user terminal
or mobile station. A communication link between two transceivers
typically includes two directional paths, e.g. Forward Link, FL,
from a base station to a user terminal, and Reverse Link, RL, from
the user terminal to the base station. Consider one path of a
communication link from a transmitter to a receiver. Four possible
configuration types for the path are given in FIG. 3: Single Input
Single Output, SISO; Single Input Multiple Output, SIMO; Multiple
Input Single Output, MISO; and Multiple Input Multiple Output,
MIMO. Each configuration type describes one path of a given
communication link, wherein the transmitter for one path is the
receiver for the other path, and vice versa.
[0063] Note that the number of receive antennas, denoted Nr, is not
necessarily equal to the number of transmit antennas, denoted Nt,
for the transmitter and/or the receiver. Therefore, a RL may have a
different configuration from that of the FL. In practice the base
station will not typically employ a single transmit antenna,
however, with the proliferation of wireless devices, particularly
for voice-only capability, single receive antennas at a user
terminal are quite common.
[0064] As illustrated in FIG. 3, a SISO configuration employs a
single transmit antenna at the transmitter and a single receive
antenna at the receiver. Further, considering a transmitter with
only a single transmit antenna a SIMO configuration employs Nr
receive antennas at the receiver, wherein Nr is greater than one,
while the transmitter has a single transmit antenna. The use of
multiple antennas at the receiver provides antenna diversity for
improved reception. Signals received by the multiple antennas at
the receiver are then processed according to a predetermined
combination technique. For example, a receiver may incorporate a
rake receiver mechanism, wherein received signals are processed in
parallel, similar to fingers of a rake. Alternate methods may be
employed specific to the requirements and constraints of a given
system and/or wireless device.
[0065] Continuing with FIG. 3, MISO configuration employs Nt
transmit antennas at the transmitter, wherein Nt is greater than
one, while the receiver has a single receive antenna. Antenna
diversity at the transmitter, such as at the base station, provides
improved reception by reducing the effects of multipath fading. The
use of multiple antennas at the transmitter introduces additional
signal paths and thus tends to increase the impact of fading at the
receiver. Diversity basically combines multiple replicas of a
transmitted signal. The combination of redundant information
received over multiple fading channels tends to increase the
overall received Signal-to-Noise Ratio (SNR).
[0066] A final configuration, MIMO, places multiple antennas at the
transmitter and receiver, i.e., Nt.times.Nr MIMO. The transmitter
may send multiple independent data streams on a same carrier
frequency to a given user. A MIMO communication link has
(Nt.times.Nr) individual links. At high SNR, the increase in
throughput approaches N times the throughput of a single transmit
system configured as a SIMO system or a system with no receive
diversity, such as a SISO system, wherein N is equal to the minimum
number of antennas at the transmitter or receiver, i.e.,
N=min(Nt,Nr).
[0067] In general diversity combining methods at the receiver fall
into one of four categories: selection; Maximal Ratio Combining,
MRC; equal gain combining; feedback diversity. Diversity combining
methods are discussed hereinbelow.
[0068] FIG. 4 illustrates configurations for mixed mode wireless
communication systems having multiple transmitter Tx antennas. A
communication link exists between each transmitter antenna and each
receive antenna. Two types of configurations are illustrated for
the various paths: MISO and MIMO. As illustrated, the transmitter
uses multiple transmit antennas for both links. Note that a
multiple access system may include all four of the configurations
of FIG. 3. As antenna diversity improves the quality of
communications and increases the capacity of a system, most
communication links will be MISO and/or MIMO. While antenna
diversity is typically assumed at the base station, in a mixed mode
system the user terminals may employ a variety of antenna
configurations and processing methods. There is a need, therefore,
for a base station to identify each type of communication link to
each user terminal and process communications accordingly. In other
words, a base station may be required to support MISO, MIMO, and
SISO configurations.
[0069] In Time Division Multiple Access, TDMA, and Frequency
Division Multiple Access, FDMA, type systems communications to a
user terminal having no receive diversity, i.e. single receive
antenna, may be segregated from other traffic. Mixed mode operation
is relatively easily accommodated in TDMA and FDMA systems. In a
spread spectrum type communication system, such as a Code Division
Multiple Access, CDMA, system, users are assigned different
spreading codes, similar in function to sub-channels in an FDMA
system or time slots in a TDMA system. The "TIA/EIA/IS-2000
Standards for cdma2000 Spread Spectrum Systems" referred to as "the
cdma2000 standard," provides a specification for a CDMA system.
Operation of a CDMA system is described in U.S. Pat. No. 4,901,307,
entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM
USING SATELLITE OR TERRESTRIAL REPEATERS," and also in U.S. Pat.
No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS
IN A CDMA CELLULAR TELEPHONE SYSTEM," both assigned to the assignee
of the present application for patent and hereby expressly
incorporated by reference.
[0070] In one embodiment of a CDMA system the spreading codes are
designed to be mutually orthogonal so as to eliminate neighbor
interference. While the communication channel is non-dispersive the
orthogonality property holds and users do not interfere with each
other. In a mixed mode system under these conditions, it is
possible to communicate on a SISO communication link using one code
and also communicates on a MISO or a MIMO communication link using
other codes. When the communication channel becomes dispersive, the
orthogonality is lost introducing interference power from other
users.
[0071] FIG. 5 illustrates one embodiment of a mixed mode system 10
having a base station, BS, 12, and four user terminals or mobile
stations, MSs, MS1 14, MS2 16, MS3 18, and MS4 20. A communication
link is illustrated between BS 12 and each of the mobile stations
14, 16, 18, 20. The BS 12 has M transmit antennas. Each
communication link includes a FL and RL. The FL communication link
configurations include a SISO configuration to MS1 14, wherein MS1
14 is a voice-only device restricted to SISO communications.
Communications to MS1 14 may be processed using a unique spreading
code to isolate the SISO communication, or alternatively may be
processed at a different carrier frequency than other traffic from
BS 12. The FL communications link with MS2 16 is a MISO
configuration, wherein MS2 16 has a single receive antenna. MS2 16
combines the multiple received signals to determine the transmitted
information. Any of a variety of methods is typically used for such
signal processing. Several combining methods are discussed
hereinbelow. The FL communication links with MS3 18 and MS4 20 are
each MIMO configurations, wherein MS3 18 has N receive antennas and
MS4 20 has M receive antennas. A variety of reception processing
methods are available for use at MS3 18 and MS4 20.
[0072] System 10 is a CDMA wireless communication system having a
channel model 22 as illustrated in FIG. 6. The channel model 22 is
used to model the communication link between BS 12 and MS4 20. A
transfer function may be used as the channel model 22, wherein the
transfer function is expressed as a set of equations describing the
link.
[0073] FIG. 7 illustrates a model 24 of a MIMO channel for
continuous time having a linear MIMO filter 26 with N.sub.Tx inputs
and N.sub.Rx outputs. The linear MIMO filter 26 is defined by the
N.sub.Tx.times.N.sub.Rx matrix H(t) comprised of linear functions
h.sub.ij(t),i=1 . . . N.sub.Tx,j=1 . . . N.sub.Rx. Generally,
h.sub.ij(t)i=1 . . . N.sub.Tx, j=1 . . . N.sub.Rx are unknown
linear functions. The linear MIMO filter 26 represents the
(N.sub.Tx.multidot.N.sub.Rx) radio channels through which the
N.sub.Tx transmit signals pass to the N.sub.Rx receiver antennas.
These radio channels are characterized by their channel impulse
responses h.sub.ij(t),i=1 . . . N.sub.Tx, j=1 . . . N.sub.Rx. The
input signal to the model, {right arrow over (x)}(t), is a
(N.sub.Tx.multidot.1) column vector representing the N.sub.Tx
band-limited transmit signals, and the output signal from the
model, {right arrow over (y)}(t), is a (N.sub.Rx.multidot.1) column
vector, sampled at t=T,2T, . . . as illustrated by switch T, where
the bandwidth of each of the transmitted signals is less or equal
to 1/T. The received signals contain additive perturbation signals
represented by the (N.sub.Tx.times.1) column vector {right arrow
over (z)}(t), introduced due to noise or co-channel interference.
The additive perturbation signals are added at summation nodes 28.
The relation between the input signals {right arrow over (x)}(t),
the channels H(t), the perturbation {right arrow over (z)}(t) and
the output signals {right arrow over (y)}(t) is given by {right
arrow over (y)}(t)=H.sup.T(t)*{right arrow over (x)}(t)+{right
arrow over (z)}(t), wherein * denotes the convolution. Alternate
models may be used to describe a channel.
[0074] For mixed mode operation of one embodiment, the base station
negotiates with user terminals to determine antenna diversity
status of the terminal. As discussed hereinabove, there are
generally four types of combination processing used at a receiver.
Selection diversity is applied at a receiver having multiple
antennas, wherein a best signal among the multiple received signals
is chosen. FIG. 8 illustrates a communication system employing
selection diversity having a transmitter 40 with one transmit
antenna 42. The transmitter 40 communicates with a rake receiver 44
having Nr fingers each coupled to an antenna in an antenna array
46. The rake receiver 44 outputs the Nr antenna signals to a
selection unit 48. The selection unit may sample the signals and
provide the best one as output, wherein the best signal is
determined by a quality metric, such as SNR. Alternate metrics may
be used based on the system configuration and constraints. The
selection diversity operation of FIG. 8 may be employed at the base
station or the mobile station.
[0075] A second method of reception diversity, referred to as MRC,
applies weights to each received signal. One embodiment of an MRC
system is illustrated in FIG. 9. The system includes a transmitter
60 having a single antenna 62. The receiver has multiple gain
amplifiers 64, each coupled to an antenna of antenna array 66. Each
received signal is weighted proportionally to the SNR value of the
signal, wherein the value of the received signal provides control
to the corresponding gain amplifier 64. The weighted values are
then summed. The individual signals are cophased by cophasing and
summing unit 68 prior to summation. The SNR of the output of the
unit 66 is equal to the sum of the individual branch SNRs, wherein
the combined SNR varies linearly with Nr, the number of receive
antennas. The MRC combination method is commonly used in CDMA
systems having rake type receivers. A third method of reception
diversity is a modification or simplification of MRC, wherein the
gains are set equal to a constant value.
[0076] A final method of reception diversity is referred to as
feedback diversity, and is similar to selection diversity. The
receiver scans received signals to determine a best signal based on
predetermined criteria. The signals are scanned in a fixed sequence
until one is found above a threshold. This signal is used as long
as it is maintained above the threshold. When the selected signal
falls below the threshold, the scanning process is performed
again.
[0077] Given the variety of wireless devices, antenna
configurations, and transmission/reception processing methods, as
well as the vagaries of individual systems, the base station
requires at least some minimum amount of information about the
receiver. Returning to FIG. 5, the BS 12 requires antenna diversity
status information on initiation of an active communication with
each of MSs 14, 16, 18, 20.
[0078] A wireless communication system, and a CDMA system
specifically, may be operated in a number of different
communication modes, with each communication mode employing
antenna, frequency, or temporal diversity, or a combination
thereof. The communication modes may include, for example, a
"diversity" communication mode and a "MIMO" communication mode.
[0079] The diversity communication mode employs diversity to
improve the reliability of the communication link. In a common
application of the diversity communication mode, which is also
referred to as a "pure" diversity communication mode, data is
transmitted from all available transmit antennas to a recipient
receiver system. The pure diversity communications mode may be used
in instances where the data rate requirements are low or when the
SNR is low, or when both are true.
[0080] FIGS. 10A and 10B illustrate a spread spectrum communication
system 200 configured for transmit diversity mode operation.
Specifically illustrated in FIG. 10A are the transmission paths for
the forward link from transmitter 202 to receiver 212. At a
transmitter 202, which may be a base station, data for transmission
is provided as individual data streams to complex multipliers 204
and 206. A unique code is applied to each of the complex
multipliers 204, 206. A first code c.sub.1 is applied to multiplier
204 and a second code c.sub.2 is applied to multiplier 206. At
multiplier 204 the signal d is spread by the code c.sub.1 and at
multiplier 206 the signal d is spread by code c.sub.2. Each of
complex multipliers 204, 206 is then coupled to a transmission
antenna 208, 210, respectively. In this way, the signal d is spread
by a unique spreading code for each antenna. The antenna 208
transmits one of the spread data signal while the antenna 210
transmits the other spread data signal. The receiver 212 includes
two antennas 214, 216.
[0081] Four transmission paths are illustrated in FIG. 10A, each
having a characteristic function, or signature, represented as
h.sub.ij, wherein i is an index corresponding to the transmit
antenna, and j is an index corresponding to the receive antenna. In
other words, a path exists for each transmit antenna-receive
antenna pair.
[0082] The data signal d may be part of a data stream, and may
represent any type of transmission information, including low
latency transmissions, such as voice communications, and high-speed
data transmissions. In one embodiment, the data stream is
packetized data, wherein individual data streams are provided to
each of multiplier 204, 206. At the receiver, the transmitted data
streams are then restored to a pre-transmission sequence. The
transmit antennas 208, 210 transmit the spread signals to a
receiver 212.
[0083] At the receiver illustrated in FIG. 10B, transmitted signals
are received at antennas 214, 216. The receiver 212 is configured
to process each of the transmission paths between transmit antennas
and receive antennas. Therefore, each of the receive antennas 214,
216 is coupled to a despread processing circuitry corresponding to
each path.
[0084] In the system 200 illustrated in FIG. 10, four paths are
provided, each having a signature or transfer function describing
the effects of the path or channel on a transmitted signal. The
four paths are despread and processed to determine four estimates
of the originally transmitted signal. The four estimates are then
summed at summation node 220 to determine a composite estimate
{circumflex over (d)}.
[0085] Each of the antennas 214, 216 is coupled to multiple
despread units, i.e. complex multipliers. A unique code c.sub.1* is
applied to despread the transmit signal that was originally spread
by code c.sub.1. A gain is applied to the resultant despread
signal, wherein the gain represents the signature of the channel
from transmit antenna 204 to receive antenna 214, h.sub.11*. The
result is an estimate of the signal d as transmitted via antenna
204 and received by antenna 214.
[0086] Antenna 214 is coupled to another multiplier for processing
the second received signal, wherein a unique code c.sub.2* is
applied to despread the signal that was spread by code c.sub.2. A
gain is applied to the resultant despread signal, wherein the gain
represents the signature of the channel from transmit antenna 206
to receive antenna 214, h.sub.21*.
[0087] Antenna 216 is configured in a similar manner for processing
signals received from transmit antennas. The estimates of each
processing path is then provided to summing node 220 to generate
the estimate {circumflex over (d)}.
[0088] Alternate embodiments may include any number of transmit and
receive antennas, wherein the number of transmit antennas may not
be equal to the number of receive antennas. The receive antennas
include processing circuitry corresponding to at least a portion of
the transmit antennas or at least a portion of the transmission
paths. The MIMO communication mode employs antenna diversity at
both ends of the communication link (i.e., multiple transmit
antennas and multiple receive antennas) and is generally used to
both improve the reliability and increase the capacity of the
communications link. The MIMO communication mode may further employ
frequency and/or temporal diversity in combination with the antenna
diversity.
[0089] FIGS. 11A and 11B illustrate a wireless system 230
configured for a MIMO mode operation. Specifically illustrated are
the transmission paths for the forward link from transmitter 232 to
receiver 250. A signal is provided to transmitter 232 as signal d
at a first data rate r. The transmitter 232 separates the signal d
into multiple portions, one corresponding to each transmit antenna
240, 242. A MUX 234 provides a first portion of signal d to
multiplier 236, labeled do, and a second portion of signal d to
multiplier 238, labeled d.sub.2. For example, each of the signal
portions d.sub.1, and d.sub.2, are provided to multipliers 236,
238, respectively, at a rate of r/2. The multipliers 236, 238 apply
spreading codes c.sub.1 and c.sub.2, respectively, to the signals
d.sub.1, and d.sub.2, respectively. The multipliers 236, 238 are
then coupled to transmit antennas 240, 242.
[0090] As illustrated in FIG. 11A, the receiver 250 includes
antennas 252, 254, wherein each antenna is coupled to two
processing paths. The signal received at antenna 252 is identified
as s.sub.1, wherein s.sub.1=h.sub.11d.sub.1+h.sub.21d.sub.2. The
transmission channel or path from transmit antenna 240 to receive
antenna 252 is described by h.sub.11 and the path from transmit
antenna 242 to receive antenna 252 is described by h.sub.21.
Similarly, the signal received at antenna 254 is identified as
s.sub.2, wherein S.sub.2=h.sub.12d.sub.1+h.sub.22d.sub.2. The
transmission channel or path from transmit antenna 240 to receive
antenna 254 is described by h.sub.12 and the path from transmit
antenna 242 to receive antenna 254 is described by h.sub.22. The
signals s.sub.1 and s.sub.2 are despread using a code c.sub.1*
corresponding to code c.sub.1 of the transmitter 232, and a code
c.sub.2* corresponding to code c.sub.2 of the transmitter 232. A
gain corresponding to each transmission path is applied to each
processing path. The results are provided to summing nodes 260 and
262, respectively, to generate estimates {circumflex over
(d)}.sub.1 and {circumflex over (d)}.sub.2. The estimates
{circumflex over (d)}.sub.1 and {circumflex over (d)}.sub.2 may
then be demultiplexed to generate an estimate {circumflex over (d)}
of the original signal d.
[0091] Specifically, transmissions sent via the transmission path
from transmit antenna 240 to receive antenna 252 are despread using
c.sub.1* corresponding to code c.sub.1 and then the gain
corresponding to h.sub.11 is applied. The result is provided to
summing node 260. In a similar way, transmission sent via the
transmission path from transmit antenna 240 to receive antenna 254
are despread using c.sub.1* corresponding to code c.sub.1 and then
the gain corresponding to h.sub.12 is applied. The result is
provided to summing node 260. In this way, the output of summing
node 260 is a composite estimate of transmissions from transmit
antenna 240.
[0092] Transmissions from transmit antenna 242 are processed in a
similar manner. Transmissions sent via the transmission path from
transmit antenna 242 to receive antenna 252 are despread using
c.sub.2* corresponding to code c.sub.2 and then the gain
corresponding to h.sub.21 is applied. The result is provided to
summing node 262. In a similar way, transmission sent via the
transmission path from transmit antenna 242 to receive antenna 254
are despread using c.sub.2* corresponding to code c.sub.2 and then
the gain corresponding to h.sub.22 is applied. The result is
provided to summing node 262. In this way, the output of summing
node 262 is a composite estimate of transmissions from transmit
antenna 242.
[0093] A detailed illustration of a wireless communication system
300 is illustrated in FIG. 12. System 300 may be operated to
transmit data via a number of transmission channels. A MIMO channel
may be decomposed into NC independent channels, with NC.ltoreq.min
{NT, NR}. Each of the NC independent channels is also referred to
as a spatial subchannel of the MIMO channel. For a MIMO system,
there may be only one frequency subchannel and each spatial
subchannel may be referred to as a "transmission channel".
[0094] A MIMO system can provide improved performance if the
additional dimensionalities created by the multiple transmit and
receive antennas are utilized. While this does not necessarily
require knowledge of CSI at the transmitter, increased system
efficiency and performance are possible when the transmitter is
equipped with CSI, which is descriptive of the transmission
characteristics from the transmit antennas to the receive antennas.
CSI may be categorized as either "full CSI" or "partial CSI".
[0095] Full CSI includes sufficient wideband characterization
(e.g., the amplitude and phase) of the propagation path between
each transmit-receive antenna pair in the NT.times.NR MIMO matrix.
Full-CSI processing implies that (1) the channel characterization
is available at both the transmitter and receiver, (2) the
transmitter computes eigenmodes for the MIMO channel (described
below), determines modulation symbols to be transmitted on the
eigenmodes, linearly preconditions (filters) the modulation
symbols, and transmits the preconditioned modulation symbols, and
(3) the receiver performs a complementary processing (e.g., spatial
matched filter) of the linear transmit processing based on the
channel characterization to compute the NC spatial matched filter
coefficients needed for each transmission channel (i.e., each
eigenmode). Full-CSI processing further entails processing the data
(e.g., selecting the proper coding and modulation schemes) for each
transmission channel based on the channel's eigenvalues (described
below) to derive the modulation symbols.
[0096] Partial CSI may include, for example, the
signal-to-noise-plus-inte- rference (SNR) of the transmission
channels (i.e., the SNR for each spatial subchannel for a MIMO
system without OFDM, or the SNR for each frequency subchannel of
each spatial subchannel for a MIMO system with OFDM). Partial-CSI
processing may imply processing the data (e.g., selecting the
proper coding and modulation schemes) for each transmission channel
based on the channel's SNR.
[0097] FIG. 12 is a diagram of a multiple-input multiple-output
(MIMO) communication system 300 capable of implementing various
aspects and embodiments of the invention. System 300 includes a
first system 310 in communication with a second system 350. System
300 can be operated to employ a combination of antenna, frequency,
and temporal diversity (described below) to increase spectral
efficiency, improve performance, and enhance flexibility. In an
aspect, system 350 can be operated to determine the characteristics
of the communication link and to report channel state information
(CSI) back to system 310, and system 310 can be operated to adjust
the processing (e.g., encoding and modulation) of data to be
transmitted based on the reported CSI.
[0098] Within system 310, a data source 312 provides data (i.e.,
information bits) to a transmit (TX) data processor 314, which
encodes the data in accordance with a particular encoding scheme,
interleaves (i.e., reorders) the encoded data based on a particular
interleaving scheme, and maps the interleaved bits into modulation
symbols for one or more transmission channels used for transmitting
the data. The encoding increases the reliability of the data
transmission. The interleaving provides time diversity for the
coded bits, permits the data to be transmitted based on an average
signal-to-noise-plus-interference (SNR) for the transmission
channels used for the data transmission, combats fading, and
further removes correlation between coded bits used to form each
modulation symbol. The interleaving may further provide frequency
diversity if the coded bits are transmitted over multiple frequency
subchannels. In accordance with an aspect of the invention, the
encoding, interleaving, and symbol mapping (or a combination
thereof) are performed based on the full or partial CSI available
to system 310, as indicated in FIG. 12.
[0099] The encoding, interleaving, and symbol mapping at
transmitter system 310 can be performed based on numerous schemes.
One specific scheme is described in U.S. patent application Ser.
No. 09/776,073, entitled "CODING SCHEME FOR A WIRELESS
COMMUNICATION SYSTEM," filed Feb. 1, 2001, assigned to the assignee
of the present application and incorporated herein by
reference.
[0100] Referring to FIG. 12, a TX MIMO processor 320 receives and
processes the modulation symbols from TX data processor 314 to
provide symbols suitable for transmission over the MIMO channel.
The processing performed by TX MIMO processor 320 is dependent on
whether full or partial CSI processing is employed, and is
described in further detail below.
[0101] For full-CSI processing, TX MIMO processor 320 may
demultiplex and precondition the modulation symbols. And for
partial-CSI processing, TX MIMO processor 320 may simply
demultiplex the modulation symbols. The full and partial-CSI MIMO
processing is described in further detail below. For a MIMO system
employing full-CSI processing, TX MIMO processor 320 provides a
stream of preconditioned modulation symbols for each transmit
antenna, one preconditioned modulation symbol per time slot. Each
preconditioned modulation symbol is a linear (and weighted)
combination of NC modulation symbols at a given time slot for the
NC spatial subchannels, as described in further detail below. For a
MIMO system employing partial-CSI processing, TX MIMO processor 320
provides a stream of modulation symbols for each transmit antenna,
one modulation symbol per time slot. For all cases described above,
each stream of (either unconditioned or preconditioned) modulation
symbols or modulation symbol vectors is received and modulated by a
respective modulator (MOD) 322, and transmitted via an associated
antenna 324.
[0102] In the embodiment shown in FIG. 12, receiver system 350
includes a number of receive antennas 352 that receive the
transmitted signals and provide the received signals to respective
demodulators (DEMOD) 354. Each demodulator 354 performs processing
complementary to that performed at modulator 122. The demodulated
symbols from all demodulators 354 are provided to a receive (RX)
MIMO processor 356 and processed in a manner described below. The
received modulation symbols for the transmission channels are then
provided to a RX data processor 358, which performs processing
complementary to that performed by TX data processor 314. In a
specific design, RX data processor 358 provides bit values
indicative of the received modulation symbols, deinterleaves the
bit values, and decodes the deinterleaved values to generate
decoded bits, which are then provided to a data sink 360. The
received symbol de-mapping, deinterleaving, and decoding are
complementary to the symbol mapping, interleaving, and encoding
performed at transmitter system 310. The processing by receiver
system 350 is described in further detail below.
[0103] The spatial subchannels of a MIMO system typically
experience different link conditions (e.g., different fading and
multipath effects) and may achieve different SNR. Consequently, the
capacity of the transmission channels may be different from channel
to channel. This capacity may be quantified by the information bit
rate (i.e., the number of information bits per modulation symbol)
that may be transmitted on each transmission channel for a
particular level of performance. Moreover, the link conditions
typically vary with time. As a result, the supported information
bit rates for the transmission channels also vary with time. To
more fully utilize the capacity of the transmission channels, CSI
descriptive of the link conditions may be determined (typically at
the receiver unit) and provided to the transmitter unit so that the
processing can be adjusted (or adapted) accordingly.
[0104] For a mixed mode system, each participant will typically
require information regarding the configuration and operating mode
of each communication link. FIG. 13 illustrates a method 400 of
negotiation for the FL, wherein the negotiation is performed at the
base station. The process starts with a query to the mobile user to
determine diversity capability information at step 402. The
diversity capability for the FL includes the number of receive
antennas used at the mobile station. Additionally, the base station
may require information about the type of combining used for
multiple receive antennas. The base station may also request
information regarding the channel quality of given link within a
same query. The base station receives the information from the
mobile station and begins determining the appropriate configuration
and processing for the FL. If the base station has a single
transmit antenna, as determined at decision diamond 404, processing
proceeds to decision diamond 408 to determine if the mobile user
has a single receive antenna or multiple receive antennas. For a FL
employing a single transmit antenna and a single receive antenna
the system is configured for SISO mode operation at step 416. SISO
mode indicates that only a single transmission stream is
transmitted from one antenna at the base station to one antenna at
the receiver.
[0105] If the base station determines that the mobile station has
multiple receive antennas at decision diamond 408, the process
continues to step 414 to configure the FL as a SIMO link. Typically
SIMO operation implies that the receiver is able to operate at a
lower Eb/No for higher data rates. In one embodiment, the SIMO link
configuration requires no further modification of the transmitter
but rather is similar to SISO when considered from the transmitter.
In an alternate embodiment, the SIMO is capable of increased data
rate, and therefore, the transmitter received feedback from the
intended receiver indicating the requested data rate. The
transmitter then adjusts for the requested data rate, such as by
adjusting modulation, coding, etc. Such adjustment of the
transmitter in response to feedback from the receiver is considered
partial CSI operation. In one embodiment, the feedback information
is provided to the base station via a real-time feedback channel
rather than being set up on initiation of a call. Returning to
decision diamond 404, if the base station has multiple transmit
antennas, the processing continues to decision diamond 406 to
determine if the mobile user has multiple receive antennas. If the
mobile station has a single receive antenna the base station
configures the link as MISO at step 412, else if the mobile station
has multiple receive antennas the base station identifies the link
as MIMO at step 410. Processing then continues to step 418 to
determine the particular mode capability of the receiver, i.e.,
spatial diversity or pure diversity. The base station then
configures the FL accordingly. A variety of indicators may be
implemented to determine the MIMO mode of operation.
[0106] In one embodiment, the base station determines the C/I of
the FL to measure link quality. The mobile station may be queried
to provide an indication of link quality, such as C/I of signals
received from the base station on the FL. The base station compares
a link quality measurement against a predetermined threshold value.
If the link quality is poor antenna diversity is used to transmit a
same data signal from multiple antennas. Note that in poor link
quality cases, the use of both transmit and receive diversity
provides an optimal solution. Such a condition could still be
viewed as a MIMO link, wherein the two basic types of MIMO links
are: pure diversity, i.e., both transmit and receive diversity; and
spatial multiplexing, i.e., parallel channels. If the link quality
is good, spatial diversity is used, else pure diversity is
applied.
[0107] FIG. 14 illustrates a corresponding method 500 of
negotiation for the RL, wherein the negotiation is performed at the
base station. The process starts with a query to the mobile user to
determine diversity capability information at step 502. The
diversity capability for the RL includes the number of transmit
antennas used at the mobile station. Additionally, the base station
may require information about the type of signal transmission used
for transmit antenna(s). The base station may also request
information regarding the channel quality of given link within a
same query. The base station receives the information from the
mobile station and begins determining the appropriate configuration
and processing for the RL. If the mobile station has a single
transmit antenna, as determined at decision diamond 504, processing
proceeds to decision diamond 508 to determine if the base station
has a single receive antenna or multiple receive antennas. For an
RL employing a single transmit antenna and a single receive antenna
the system is configured for SISO mode operation at step 516. SISO
mode indicates that only a single transmission stream is
transmitted from one antenna at the mobile station to one antenna
at the base station.
[0108] If the base station has multiple receive antennas at
decision diamond 508, the process continues to step 514 to
configure the RL as a SIMO link (again, nothing special needs to be
done over SISO). Further processing, described hereinbelow,
verifies the quality of the link to determine an appropriate
configuration.
[0109] Returning to decision diamond 504, if the mobile station has
multiple transmit antennas, the processing continues to decision
diamond 506 to determine if the base station has multiple receive
antennas. If the base station has a single receive antenna the
process configures the link as MISO at step 512, else if the base
station has multiple receive antennas the process identifies the
link as MIMO capable at step 510. Processing continues to step 518
to select a mode of operation as spatial diversity or pure
diversity. As described hereinabove, the decision may be made in
response to a variety of indicators.
[0110] In a mixed mode system, the base station configures the
system for the appropriate communication for each link. The base
station may also provide instructions to the remote station
indicating the type of reception processing to apply. MIMO
processing can spread signals for each individual communication
link with a unique spreading code, but transmits to all links on
all antenna elements. A variety of methods are available for SO
processing, i.e., MISO and/or SISO processing. One method using two
transmit antennas is described in "A Simple Transmit Diversity
Technique for Wireless Communications" by Siavash M. Alamouti, IEEE
JOURNAL ON SELECT AREAS IN COMMUNICATIONS, VOL. 16, NO. 8, OCTOBER
1998, pp. 1451-1458, which is hereby expressly incorporated by
reference. A transmit diversity scheme is applied to a
configuration of two transmit antennas and one receive antenna. The
receive antenna employs an MRC type reception diversity method.
[0111] One embodiment of a system using this method is illustrated
in FIG. 15. A system 600 includes transmit antennas 602, 604 in
communication with receive antenna 606. Receive antenna 606 is
coupled to channel estimator 608 and to combiner 610, which are
each coupled to maximum likelihood detector 612. Operation is
defined by the encoding and transmission sequence of information
symbols at the transmitter, the combining scheme at the receiver,
and the decision rule for the maximum likelihood detector. Signals
are transmitted from antennas 602, 604 in the order indicated.
[0112] The antennas 602 and 604 create transmit vectors as
illustrated in FIG. 15. At a first time antenna 602 transmits s0
while antenna 604 transmits s1. At a second time antenna 602
transmits -s1* while antenna 604 transmits s0*, wherein * denotes
the complex conjugate operation. The channel at a time t is then
modeled by h.sub.0=.alpha..sub.0.theta..sup.j- .theta..sup..sub.0
and h.sub.1=.alpha..sub.1.theta..sup.j.theta..sup..sub.- 1.
[0113] The channel estimator 608 provides h.sub.0 and h.sub.1 to
combiner 610 and to maximum likelihood detector 612. From the
values of h.sub.0 and h.sub.1, the combiner 610 forms two combined
signals {overscore (s)}.sub.0 and {overscore (s)}.sub.1 to provide
to the maximum likelihood detector 612. The received signals at the
channel estimator 608 and combiner 610 are given as
r.sub.0=h.sub.0s.sub.0+h.sub.1s.sub.1+n.sub.0, and
r.sub.1=-h.sub.0s.sub.1*+h.sub.1s.sub.0*+n.sub.1, wherein n.sub.0
and n.sub.1 represent injected noise terms for each path. Noise
injection may be introduced between receive antenna 606 and channel
estimator 608. The first signal {overscore (s)}.sub.0 is calculated
as h.sub.0*.multidot.r.sub.0+h.sub.1.multidot.r.sub.1*, and the
second signal {overscore (s)}.sub.1 is calculated as
h.sub.1*.multidot.r.sub.0-h- .sub.0.multidot.r.sub.1*.
[0114] As illustrated in FIG. 15, the channel estimates h.sub.0 and
h.sub.1 and the signals {overscore (s)}.sub.0 and {overscore
(s)}.sub.1 are provided to the maximum likelihood detector 612. A
selection decision rule is applied to the signals {overscore
(s)}.sub.0 and {overscore (s)}.sub.1 by maximum likelihood detector
612. With Nt=2 and Nr=M, the configuration and method provides
diversity order of 2M, i.e. 2M communication links.
[0115] The system 600 of FIG. 15 may be extended to incorporate
multiple receive antennas, wherein channel estimation is made for
each communication link from a transmitter to a receiver. The
channel estimates are then provided to a combiner, wherein the
selection criteria is applied to the communication links.
[0116] Further, operation of the system of FIG. 15 may be extended
to employ a combination of Walsh functions. FIG. 16 illustrates a
non-Channel State Information, or non-CSI, type transmitter modem
architecture 700 according to one embodiment. A non-CSI modem does
not rely on substantial channel state information at the
transmitter. The architecture establishes orthogonality among the
signals transmitted on multiple transmit antennas by applying Walsh
functions to the transmit signals. The transmit orthogonality
provided by the Walsh functions can be used to increase bandwidth
efficiency by transmitting distinct transmit signal symbols on each
antenna. As illustrated in FIG. 16, modem 700 includes a trellis
coding unit 702 coupled to a modulator 704, such as a Quadrature
Amplitude Modulator. Alternate embodiments may use an alternate
type of modulator. The modulated signal is provided to one of
multiple antennas (not shown) by way of a switch 706. Each antenna
is coupled to a corresponding multiplier 708. The signals are
routed to multipliers 708 for application of a unique Walsh code.
The switch 706 coupled the output of the modulator 704 to each of
multipliers 708, and thus antennas, one at a time.
[0117] The modem architecture of FIG. 16 increases of the
efficiency of the transmission coding and reception processing of
FIG. 15. As an example, consider the transmission of two symbols,
denoted A and B. The transmitter creates two transmit vectors
x.sub.1=[A B*].sup.T and x.sub.2=[B-A*].sup.T. A different Walsh
code is applied to each vector. The elements of the two vectors are
then transmitted sequentially on the two antennas, respectively.
Consider a configuration as illustrated in FIG. 15 having two
transmit antennas and one receive antenna. The receiver may
construct estimates of the two transmitted symbols applying the
appropriate Walsh codes.
[0118] In an alternate embodiment, each of the multipliers 708 is
coupled directly to QAM 704 without the switch 706. The transmit
signal symbols are repeated across the transmit antennas, wherein
each symbol is spread with a different Walsh sequence at each
antenna. The resulting orthogonality may be used to establish full
transmit diversity across all transmit antennas.
[0119] An alternate method of diversity processing is detailed in
"A Novel Space-Time Spreading Scheme for Wireless CDMA Systems," by
B. M. Hochwald, et al., Thirty-seventh Annual Allerton Conference
on Communication, Control and Computing, Sep. 22-24, 1999, pp.
1284-1293, which is expressly incorporated herein by reference.
Transmit diversity at the base station is enhanced by space-time
spreading of transmit signals. According to one embodiment, this
method specifies the form of transmit signals and the type of
coding. Each transmit signal is spread across different antenna
elements. For the case of two transmit antennas and one receive
antenna, two spreading codes are used. Both spreading codes are
applied to both transmit symbols. The transmitted signals are given
as t.sub.1=(1/{square root}{square root over
(2)})(b.sub.1c.sub.1+b.sub.2c.sub.2) and t.sub.2=(1/{square
root}{square root over (2)})(b.sub.2c.sub.1-b.sub.1c.sub.2),
wherein b.sub.1 and b.sub.2 are data symbols, and c.sub.1 and
c.sub.2 are spreading codes. The receiver uses the codes c.sub.1
and c.sub.2 to despread the received signals.
[0120] Still another method of antenna diversity is disclosed in
U.S. Pat. No. 5,280,472, "CDMA MIOCROCELLULAR TELEPHONE SYSTEM AND
DISTRIBUTED ANTENNA SYSTEM THEREFOR," by Klein S. Gilhousen, issued
Jan. 18, 1994, assigned to the assignee hereof and hereby expressly
incorporated by reference. A system 800 as illustrated in FIG. 17
having a distributed antenna architecture communicates with mobile
users in a CDMA communication system. The mobile users may employ
any of a variety of antenna configurations. The system 800 includes
a transceiver which receives an encoded signal for transmission and
performs frequency conversion of the encoded signal to generate a
Radio Frequency, RF, signal. The transceiver 802 provides the RF
signal to a distributed antenna system 804 having antenna elements
806, 808, 810, . . . , 812 coupled in series. Delay elements 814,
816, 818, . . . are disposed between adjacent antenna elements 806,
808, 810, . . . , 812. The delay elements 814, 816, 818, . . .
provide a predetermined delay (typically greater than 1 chip) to
signals transmitted from each of antennas 806, 808, 810, . . . ,
812. The delayed signals provide multi-paths which facilitate
signal diversity for enhanced system performance.
[0121] Alternate embodiments may provide transmit diversity and/or
reception diversity according to a variety of configurations and
methods. In each of these situations, the base station determines
the configuration and requirements of each communication link. The
base station may require additional information from a given mobile
user, and similarly, may need to transmit specific processing
information to one or all mobile users. The base station may select
among a variety of transmission scenarios based upon constraints of
a given communication link or some other criterion. In one
embodiment, the base station determines the transmission scenario
in response to quality of the communication link channel. An
alternate embodiment seeks to achieve a desired signal error
rate.
[0122] FIG. 18 illustrates base station 900 according to one
embodiment having multiple antennas 902, including multiple
transmit and receive antennas. Note that FIG. 18 circuitry may be
applied to a remote station as well. Alternate configurations may
employ separate receive antennas and transmit antennas. As
illustrated, a communication bus 916 provides interface within the
base station 900 for the central processor 912, the memory device
914, the antenna diversity controller 906, the modem 910 and the
error coding and status unit 908. The transceiver 904 coupled to
antennas 902 prepares signals for transmission. The transceiver 904
is coupled to antenna diversity controller 906 and modem 910.
[0123] The base station 900 determines a transmission scenario on
initiation of each communication link. Initiation refers to the
start of a communication, including, but not limited to, response
to a paging message from the base station, or a request for a
communication from a mobile user. Within the base station 900,
diversity control decisions are processed by central processor 912
according to computer-readable instructions stored in the memory
device 914. Diversity control instructions may be stored in memory
device 914 and/or antenna diversity controller 906. Decision
criteria, such as used for maximum likelihood decisions, may be
stored in memory device 914 and/or antenna diversity controller
906, wherein the decision criteria may be dynamically adjusted in
response to the communication environment, etc.
[0124] For a given communication link, the antenna diversity
controller 906 determines the type of configuration and processing,
i.e. transmission scenario. For MIMO configurations, the antenna
diversity controller 906 applies a common transmission scenario to
each of the multiple transmit antennas 902. In one embodiment, a
default scenario is used, while in alternate embodiments, the
scenario is selected from multiple options.
[0125] The base station 900 performs the methods 400 and 500 of
FIGS. 13 and 14, respectively, to determine an appropriate
transmission scenario. Basically, according to one embodiment, the
method extracts antenna diversity status information from the other
participant to a communication. The information is processed to
determine an appropriate, available transmission scenario. The
transmission scenario may be simple or complex, depending on the
system capabilities. The methods 400, 500 may be stored in
computer-readable instructions stored in memory device 914 or in
antenna diversity controller 906. In response to the selection, the
modem 910 encodes the baseband data symbols as instructed by the
antenna diversity controller 906. In one embodiment, the antenna
diversity status is a FL diversity indicator indicating a MISO or a
MIMO configuration. In an alternate embodiment, the antenna
diversity status includes a RL diversity indicator indicating a
SIMO or a MIMO configuration. In a simple form, the FL and RL
diversity indicators may be one bit, wherein assertion indicates
multiple antennas at the mobile user associated with the
corresponding path, and negation indicates a single antenna. The
antenna diversity status may include a variety of information, and
may be sent as a message to the base station 900. For a given
mobile user, the antenna diversity status may include the number of
transmit antennas, the number of receive antennas, the reception
diversity configuration, as well as other parameters of the mobile
user. The base station 900 uses some or all of this information in
selecting a transmission scenario for the mobile user, i.e., for a
given communication link.
[0126] Once the base station has selected a transmission scenario,
the antenna diversity controller 906 may send operating
instructions to the mobile user. The base station may identify one
of a set of predetermined scenarios to provide reception handling
including, but not limited to, the form of equations used to
generate the transmitted signals, selection decision criteria,
number of transmitting antennas, etc. Similarly, the base station
900 may instruct the mobile user as to a transmission scenario for
the RL. The confirmation may be in the form of a message
transmitted to the mobile user, or may be broadcast to all
users.
[0127] A variety of antenna diversity scenarios are available for
processing communications to a receiver having only a single
antenna. Embodiments may employ any number and/or combination of
such scenarios. Similarly, negotiations between the transmitter and
receiver for a given path of a communication link may be processed
in a variety of ways. According to one embodiment, the antenna
diversity status information is transmitted according to a
predetermined format and/or protocol. An alternate embodiment
allows the transmitter to query the receiver for individual
diversity parameters, such as the number of receive antennas, the
configuration and/or spacing of antennas, reception diversity
handling specifics, etc. Still other embodiments allow the receiver
to query the transmitter for specific information. Typically,
antenna diversity negotiations are performed at initiation of a
communication, however, alternate embodiments may allow adjustment
during a communication, wherein the quality of the communication
link channel degrades over time and environmental condition.
[0128] Implementation of spatial diversity in a wireless
communication system requires consideration of those mobile
stations that lack the capability of processing the multiple
transmitted signals, e.g., a SISO unit. A brute force method
assigns a carrier frequency to the SISO capable mobile station
different from other carriers used in the system. A smart diversity
solution, as described hereinabove, incorporates an algorithm or
other method or technique that accommodates single receive antenna
users in a mixed mode system. An alternate method placing less
demand on the bandwidth usage of the system incorporates delay
transmit diversity, wherein the signal intended for the SISO
capable mobile station is transmitted via each antenna with a
delay. This provides sufficient energy to prevent jamming the
signal provided to the SISO user.
[0129] According to one embodiment of spatial diversity in a mixed
mode system, illustrated in FIG. 19, a base station 1000 is adapted
to communicate in a mixed mode system. For example, base station
1000 may communicate with mobile station 1012 that is SISO capable
and base station 1000 may communicate with mobile station 1014 that
is MIMO capable. The mobile station 1012 is specifically not
capable of receiving signals from a transmitter employing transmit
diversity. This implies that mobile station 1012 has a single
receive antenna and is not adapted with any software, hardware, or
other means for signals processed using transmit diversity. The
mobile station 1012 is a basic SISO device. The MIMO capable mobile
station 1014 may include a combination of multiple receive
antennas, rake type receiver circuitry having the ability to
combine multiple received signals, software and/or hardware for
implementing a smart diversity method such as described
hereinabove.
[0130] For optimum operation, the base station 1000 desires to
transmit to MIMO capable mobile station 1014 using a spatial
diversity or pure diversity technique, however, such transmissions
from multiple antennas will introduce interference to SISO capable
mobile station 1012. As discussed hereinabove the SNR of a received
signal in a SISO communication, wherein the receiver includes a
rake type receiver, is given as: 5 SISO = ( W I o R ) [ + I 0 + + I
0 ] . ( 5 )
[0131] The interference power in the denominator of the first term
in square brackets of equation (5) is identically correlated with
the signal power of the second term. Assuming the data rate and
power allocation are matched appropriately, the interference power
caused by the delay spread does not significantly contribute to the
overall error rate. That is, the primary error event is when both
paths fade into the noise.
[0132] When the transmitter introduces an additional transmit
antenna to accommodate users employing MISO and/or MIMO, such a
second transmit antenna results in a channel response to the SISO
user of H.sub.1(t)=h.sub.1,0(t)+h.sub.1,1(t-T), and the SNR at the
rake type receiver output now becomes: 6 mixed_mode = ( W I o R ) [
+ I 0 + I 1 + + I 0 + I 1 ] . ( 6 )
[0133] Inspection of the SISO SNR expression of equation (6) shows
that the power from the additional transmit antenna presents an
independent fading interference term in the denominator of both
terms in the brackets. In this case, the primary error event is the
desired signal from antenna 0 fading relative to the interference
power emitted from an additional antenna. As in mixed mode
operation (e.g., one transmitter having communicating with a MIMO
and/or MISO user and also with a SISO user), the interference power
from the additional antennas can seriously degrade the performance
of the SISO user.
[0134] In order for base station 1000 to transmit to both mobiles
1012 and 1014 using spatial diversity, i.e., multiple antennas,
base station 1000 implements a delay in signals to the mobile
station 1012 from multiple antennas. The provision of multiple
copies of the signal intended for the SISO capable mobile station
1012 provides additional signal energy needed to prevent jamming
caused by the transmissions from the multiple antennas.
[0135] As illustrated in FIG. 19, base station 1000 includes
antennas 1008, 1010, wherein alternate embodiments may include any
number of antennas. A first signal intended for MIMO capable mobile
station 1012 is labeled SIGNAL 1, wherein this signal is provided
to antenna 1008 of base station 1000. A second signal intended for
the same MIMO capable mobile station is labeled SIGNAL 2, wherein
this signal is provided to antenna 1010 of base station 1000.
[0136] The signal intended for SISO mobile station 1012 is labeled
SIGNAL 3, wherein this signal is provided to antenna 1008 via node
1002. SIGNAL 3 is provided to antenna 1010 as a delayed signal,
wherein SIGNAL 3 is provided to delay element 1004 and then to node
1006. For embodiments having more antennas than illustrated in FIG.
19, additional antennas may each have associated delays
[0137] The mobile station 1012 then receives the SIGNAL 3
transmitted from antenna 1008 and the delayed version of SIGNAL 3
from antenna 1010. The energy of the delayed version of SIGNAL 3
from antenna 1010 provides energy to balance the effects of other
energies from other signals generated by the antenna 1008. The
effective SNR at the output of the SISO RAKE receiver in this case
for the two path channel model considered above is then given by: 7
mixed_mode = ( W R ) [ I o + I 0 + I 1 + I o + I 0 + I 1 + a I 1 +
I 0 + bI 1 + b I 1 + I 0 + aI 1 ] , where a = E { h 1 , 0 2 } , and
b = E { h 1 , 1 2 } . ( 9 )
[0138] According to one embodiment, a mobile station is capable of
operating in a variety of transmission scenarios.
[0139] As illustrated in FIG. 20, mobile station 1100 includes a
receive antenna array 1102 coupled to a receiver 1104. In one
embodiment, the receiver 1104 is a transceiver. The receiver 1104
is then coupled to a channel quality measurement unit 1106. The
mobile station 1100 measures a parameter associated with the
channel quality, such as C/I, and makes a decision regarding
receive processing based thereon. In general, the mobile station
makes a data rate determination based on the channel quality,
interference plus noise level and possibly other criteria. The
mobile station conveys information to the base station(s)
describing the preferred transmission mode. The decision determines
which transmission scenario will be implemented by the antenna
diversity controller 1108 for the channel.
[0140] Within mobile station 1100, modules communicate via a
communication bus 1116. Instructions may be stored in a memory
storage device, such as memory device 1114. A central processor
1112 controls operation within the mobile station 1100. In one
embodiment, a look up table is provided in the memory device 1114,
wherein entries associate a transmission scenario with multiple
channel quality measures. Alternate embodiments may use other
measures of channel quality, sufficient to provide information for
determining a transmission scenario.
[0141] As described hereinabove, a base station often operates in a
wireless communication system that may include a variety of
different receivers, i.e. mobile stations, etc. To handle
transmissions to a SISO receiver, the base station determines a
transmission scenario. The transmission scenario may be a diversity
technique, such as described by Walsh or Alamouti, as described
hereinabove, a pure diversity approach, or a combination of these.
Similarly, the base station may implement a transmission scenario
that uses delays, as described hereinabove. In order to achieve a
high data rate, alternate embodiments implement a spatial
multiplexing scenario wherein redundant data is transmitted. The
base station selects a transmission scenario based on the resources
of the base station and the receiver. The resources of the receiver
may be provided when the receiver registers with the base station,
or the base station may query the receiver for such information.
The base station then implements a scenario.
[0142] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0143] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein may
be implemented as electronic hardware, computer software, or
combinations of both. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled artisans may implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present invention.
[0144] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a Digital Signal Processor, DSP, an Application Specific
Integrated Circuit ASIC, a Field Programmable Gate Array FPGA or
other programmable logic device, discrete gate or transistor logic,
discrete hardware components, or any combination thereof designed
to perform the functions described herein. A general purpose
processor may be a microprocessor, but in the alternative, the
processor may be any conventional processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0145] The steps of a method or algorithm described in connection
with the embodiments disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module may reside in Random
Access Memory, RAM, flash memory, Read Only Memory, ROM, Erasable
Programmable ROM, EPROM, Electrically Erasable Programmable ROM,
EEPROM, registers, hard disk, a removable disk, a Compact Disk or
CD-ROM, or any other form of storage medium known in the art. An
exemplary storage medium is coupled to the processor such the
processor can read information from, and write information to, the
storage medium. In the alternative, the storage medium may be
integral to the processor. The processor and the storage medium may
reside in an ASIC. The ASIC may reside in a user terminal. In the
alternative, the processor and the storage medium may reside as
discrete components in a user terminal.
[0146] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
* * * * *